Not applicable.
Fuel cells are devices that react a fuel and an oxidant to generate electricity. Many fuel cells use H2 as a fuel and oxygen or air as an oxidant. The production of H2 typically involves reforming or partial oxidation of a hydrocarbon source to produce an impure H2 stream called synthesis gas. The synthesis gas is traditionally upgraded to pure H2 (99.9+%) using a pressure swing adsorption process. However, fuel cells do not require a pure H2 fuel. The fuel H2 used in a fuel cell does have to be CO-free because CO degrades performance of the cell. Hence, the objective of this invention is to provide an improved process for the production of CO-free H2 that can be used in fuel cell applications.
There is prior art on the production of electricity from fuel cells using H2 as a fuel. In much of the art, the removal of CO from H2 is an important and necessary step in the process. Some of the previous approaches to CO removal are noted below.
U.S. Pat. No. 4,522,894 teaches a process for electric power generation using fuel cells in which a hydrocarbon liquid is passed through an autothermal reactor with 2 different types of catalysts. The synthesis gas produced is then sent to high temperature and low temperature shift reactors which convert CO and water into CO2 and H2. The CO-free H2 produced by shift conversion is then sent to the anode of the fuel cell. Thus, in this art, CO is removed by the catalytic water gas shift reaction.
U.S. Pat. No. 4,532,192 describes a fuel cell system wherein the gas exhausted from the anode section is applied to a gas separation means in which the gas separation means acts to remove unused fuel process gas from the exhaust gas to the exclusion of other gas components. The removed fuel gas, no longer diluted by other gas constituents, is then applied as input fuel to the anode section of the fuel cell. As in the ""894 patent, CO removal from the synthesis gas is accomplished by the catalytic shift reaction.
U.S. Pat. No. 5,330,727 describes an apparatus for removal of CO from gaseous media. CO present in gaseous media is diminished by selective oxidation in the presence of oxygen. The oxidation of CO is accomplished in a staged manner. The first CO oxidation occurs at a high temperature to avoid catalyst deactivation then through a second catalyst bed at lower temperature to ensure essentially complete CO removal.
U.S. Pat. No. 5,604,047 comprises a method for lowering the CO content of a CO-containing H2-rich gas stream by contacting the gas stream with an adsorbent capable of preferentially adsorbing CO. The adsorbents employed consist of platinum, palladium, ruthenium, rhenium, iridium, the carbides and nitrides of tungsten, molybdenum, vanadium, chromium, tantalum and mixtures thereof. This is a 2-bed system and the preferred desorbing gas is steam.
The prior art of fuel cell feed gas preparation suffers from inefficiencies, the need for expensive catalysts and multiple stage processing. These deficiencies make such processes unattractive for the economic use of fuel cells to replace traditional sources of electricity and motive power such as vehicles, where low cost, simplicity and efficiency is important for consumer acceptance. The present invention overcomes the drawbacks of the prior art with an inexpensive, efficient and simple method for providing hydrogen fuel for a fuel cell which is purified of the most deleterious contaminant, carbon monoxide, as well as water.
The present invention is a method for production of a hydrogen-rich fuel gas compatible for a fuel cell, comprising; reforming a hydrocarbon-containing fuel to a CO-containing, hydrogen-rich reformate, converting CO in the reformate to CO2 and hydrogen by a catalyzed water-shift reaction, removing residual CO in the reformate by adsorption on a copper halide adsorbent, and passing the essentially CO-free reformate as a hydrogen-rich fuel gas to a fuel cell.